1. Field of the Invention
The present invention relates to an ellipsograph for drawing an ellipse, and more particularly, the present invention relates to an ellipsograph which has a simple structure and includes a base member for defining a fixed base of a triangle and an ellipse drawing frame and an ellipse deriving thread for cooperatively enabling an elliptic locus to be drawn through the movement of a vertex of the triangle, whereby an ellipse having a variety of sizes can be conveniently drawn on the basis of a fundamental mathematical principle in association with geometrical forming of the elliptic locus.
2. Description of the Related Art
Generally, with an ellipse means, as shown in FIG. 1, a closed loop of an elliptic locus is generated by continuous movement of a vertex c of a triangle abc around an origin O on an x and y coordinate plane in a state wherein a length of each of two focal distances ac and bc is changed and the total length of the two focal distances ac and bc is not changed when a base ab of the triangle abc is fixedly given in a direction of a major axis as a distance between two foci of the ellipse.
The ellipse has a major axis 2r.sub.1 and a minor axis 2r.sub.2. When considering distances from the origin 0 of the x and y coordinate plane, that is, a semi-major axis r.sub.1 and a semi-minor axis r.sub.2, the semi-major axis r.sub.1 indicates a length when the focal distances ac and bc are aligned in line with the x axis together with the base ab of the triangle abc, and the semi-minor axis r.sub.2 indicates a height of the triangle abc when the focal distances ac and bc of the triangle abc form equilaterals of an isosceles triangle abc.
Due to aforementioned geometry of the ellipse, it is impossible to draw an ellipse with compasses for simply drawing a circle. From this standpoint and to cope with the problem, a plurality of ellipsographs are disclosed in the art.
As an example, an ellipsograph which is described in Korean Utility Model Application No. 87-13242, includes a support bar for defining a semi-major axis of an ellipse. The support bar is fixed by means of a left and right moving section and a major axis-adjusting thread which serve to maintain an elliptic locus. Then, a length of the major axis-adjusting thread is adjusted to draw an ellipse having a desired size, with the length then fixed. Thereupon, in the left and right moving section, as a moving segment and writing means which is coupled to the moving segment are simultaneously moved, an elliptic circumference is drawn by the writing means.
Further, another ellipsograph which is described in Korean Utility Model Application No. 78-4761, includes parent compasses which are rotated around a bevel gear. A foot plate which is to be fixed on a plane of a drawing sheet, is threaded into the bevel gear. The ellipsograph further includes son compasses which are rotated around one end of the parent compasses by an angle which is two times that of the rotation angle of the parent compasses. In this state, if the parent compasses are rotated by 360.degree., a center shaft is rotated and bevel gears are meshed with each other to be operated in an interlocked manner. Accordingly, another bevel gear which does not define a major axis, is rotated, and by this, the son compasses are rotated by an angle of 720.degree. in a direction which is opposite to the rotating direction of the parent compasses, whereby drawing of the ellipse is effected.
As described above, with an ellipse means, an elliptic locus is generated by continuous movement of a vertex of a triangle in a state wherein a length of each of two focal distances is changed and the total length of the two focal distances is not changed when a base of the triangle is fixedly given as a distance between two foci of the ellipse. As a tool for drawing an ellipse, a multitude of ellipsographs which use a gearing mechanism or the like, are disclosed in the art.
However, the ellipsograph using the gearing mechanism or the like has a problem in that its structure is complicated and manipulation thereof is cumbersome. Also, even in the case of an ellipsograph using an adjusting string, an upper elliptic circumference must be first drawn, and then, after the ellipsograph is returned to its original position, a lower elliptic circumference must be drawn, whereby drawability of the ellipse is deteriorated.
Moreover, if an ellipsograph is used for teaching a fundamental mathematical principle of an ellipse, for example, in the elementary geometry, it is difficult with the conventional ellipsograph to prove the fact that with an ellipse means an elliptic locus is generated by continuous movement of a vertex of a triangle in a state wherein a length of each of two focal distances is changed and the total length of the two focal distances is not changed when a base of the triangle is fixedly given as a distance between two foci of the ellipse.